FAMILY I. THIOEHODACEAE 6\) 



Key to the genera of family Thiorhodaceae. 



I. Cells usually combined into aggregates. 



A. Cells grouped as regular sarcina packets. 



Genus I. TMosarcina, p. 39. 



B. Cells not in sarcina packets. 



1. Aggregates in the form of a flat sheet. 



a. Cells in regular arrangement, with tetrads as the common structural unit. 

 Genus II. Thiopedia, p. 40. 

 aa. Cells in irregular aggregates. 



Genus III. Thiocapsa, p. 41. 



2. Aggregates in the form of three-dimensional masses. 



a. Cells distinctly rod-shaped and arranged in a net-like structure. 

 Genus IV. Thiodictyon, p. 41. 

 aa. Cells not so arranged. 



b. Cells in a common capsule, individuals rather scattered and loosely 

 grouped. 



Genus V. Thiothece, p. 42. 

 bb. Cells in rather dense clumps. 



c. Aggregates embedded in conspicuous common slime capsule. 



d. Aggregates small, compact, often several of them enclosed to- 

 gether in a common capsule. 



Genus VI. Thiocystis, p. 42. 

 dd. Aggregates large and solid, later break up into small clusters. 

 Genus VII. Lamprocystis , p. 43. 

 cc. Common capsule lacking or verj^ transient. 



d. Aggregates as a whole exhibit amoeboid movements. 

 Genus VIII. Amoebobacter, p. 44. 

 dd. Aggregates devoid of amoeboid movements. 



Genus IX. Thiopoly coccus, p. 45. 

 II. Cells usually occurring singly. 



A. Cells clearly spiral-shaped. 



Genus X. Thiospirillum, p. 46. 



B. Cells not spiral-shaped. 



1. Cells irregular, often swollen, distorted, or composed of long, crooked and bent 

 rods to filaments. 



Genus XI. Rhabdomonas , p. 48. 



2. Cells regular, spherical to short rods or bean-shaped. 



a. Cells spherical, as a rule non-motile, and each one surrounded by a rather 

 wide capsule. 



Genus XII. Rhodothece, p. 50. 

 aa. Cells ellipsoidal, ovoid, short rods or vibrios, actively motile. 

 Genus XIII. Chromatium, p. 50. 



Genus I. Thiosarcina Winogradsky, 1888. 



(Zur Morphologie und Phj'siologie der Bacterien, I. Schwefelbacterien, Leipzig, 1888, 

 104.) 



Thi.o.sar.ci'na. Gr. noun thium sulfur; M.L. fem.n. Sarcina a genus of bacteria; M.L. 

 fem.n. Thiosarcina sulfur Sarcina. 



Individual cells spherical, forming regular cubical packets of sarcina-shape, resulting 

 from consecutive division in three perpendicular planes. Packets commonly containing 

 8 to 64 cells. Infrequently motile. Non-spore-forming. Contain bacteriochlorophyll and 



